Apr/May 2007 - Barung Landcare

Biological Control of
Weeds – Why and How
WEED WATCH by John Wightman
Blackall Range Weeds Task Force
As I see it, plants become weeds for two reasons. Firstly,
they live in an environment that really suits them, in terms of
soil conditions, rainfall and temperature. Secondly, they are,
to a large extent, unregulated by natural control factors. This
means they have few or no serious pathogens (fungal, viral
or bacterial diseases) or arthropod or mammal defoliators,
leaf miners, seed and stem borers, gallers, root eaters, etc.
Going a little further, we can observe that weeds have come
from overseas without bringing old or being found by new
natural enemies. Alternatively, they may have colonised an
environment which has been modified in such away that
populations of natural control agents have been seriously
challenged. Flood, fire, erosion, land clearing and cultivation
can open up land to ‘unopposed’ weed invasions.
One of the tools available to the managers of our natural
resources is the creation of a cadre of natural enemies
that can exploit the weed as a food source. When this is
successful, we call it biological control. Biological control is
most likely to succeed when integrated with other resource
management tools, such has strategic herbicide application,
grazing management, burning, and the prevention of
spread.
Biological control projects are lengthy and expensive
processes and are the realm of the public sector. In Australia
this means CSIRO, various State Departments and a host of
international counterparts. Once the decision is made to go
ahead, continuity needs to be guaranteed until the project is
fully successful or until it is clear it will not succeed.
The first job is to trace the centre of origin of the weed. This
not always easy because some species have tracked through
several continents – for instance, as seeds on the tools and
clothing of gold miners. Then the life system of the target
species is investigated in its native country, in climate zones
akin to where it has established in Australia.
Any diseases or herbivores that appear to keep the target
in check in its native environment are classified as a
‘potential biohazard’. Then these species are subjected to
intensive checks to ensure they will have no deleterious
effect on native flora and fauna if they are introduced. Some
conservationists feel that no species should be introduced,
because it is not possible to test widely enough to guarantee
safety. This is acknowledged, but the risk is balanced against
the benefit to the common good of reducing the impact of
a given weed species. These tests are carried out overseas
or in strict quarantine in Australia.
A target species will, of necessity, be bred through a number
of generations before release. This should guarantee that it
is not carrying parasites or pathogens (even pathogens have
pathogens). There is then the risk that the organisms will
become adapted to life in a protected environment and may
not establish in the wild.
What a lot of hoops, and there are still more! Once a
potential biocontrol agent has been deemed safe for release,
it has to be multiplied, distributed and monitored. There
are no catchall rules of procedure – each scenario opens a
new book.
What is clear is that releases have to be monitored well,
so as to learn from successes and failures. At this point
the ownership of the project really needs to pass from
government bodies to interest groups within the regional
natural resource management administrations (RNRMA).
Hopefully, support for training and facility development
is being taken on board by the RNRMAs, so that the final
stage in these long and expensive processes is in the hands
of the people on the land who will benefit most.
For more info, see www.weeds.crc.org.au
WEED FOLDERS
For loan or viewing at Barung
‘BOOK REVIEW’ by Lin Fairlie
To fill a recognised gap in comprehensive weed information,
Caloundra City Council has compiled a large folder,
the Weeds Awareness and Information Kit, and has provided
two copies to Barung.
Each kit consists of two copies of the ‘Weeds Awareness
and Information Kit’ CD, a copy of a booklet prepared by
the coastal councils and Greening Australia for coastal areas,
and a copy of an informative booklet, Plants and fungi poisonous
to people in Queensland, from the Queensland State
Government.
The remainder of this large kit contains a comprehensive
set of the ‘Weed Fact Sheets’ produced by the Department
of Natural Resources, Mines and Water. These sheets cover
which chemicals and techniques are best for managing a
particular weed, which is very useful. Water weeds are also
covered, which some landholders will find invaluable. Information
about some of the lesser known ‘garden escapees’ are
also included, and will be very timely after our recent good
rains. Do you have ‘polka dot plant’ (also known as ‘freckle
face’)? My neighbour does and now I have a carpet of it.
Also included is a list of the 200 most invasive environmental
weeds in south-east Queensland. A foldout sheet called
‘Understanding pest plants’ presents in a colourful way the
various relationships between pest plants, their transport, and
people’s actions. The final sheet covers ‘Understanding the
mechanisms behind herbicide resistance’, explained through
a series of diagrams.
The CD covers all of the fact sheets alphabetically, accompanied
by suggestions for managing particular weeds.
Another folder held by Barung, the Introductory weed
management manual from the CRC for Weeds, is aimed at
tertiary students but landholders could find parts of it very
instructive. It consists of four well laid out modules, but does
not have a CD.
Barung has four copies of the CD from the Weeds Awareness
and Information Kit available to members for weekly borrowing
(by signing the borrowing register). The large folders
can be perused at Barung only.
13